Various materials, in which layers with high function, for example, an electrode layer, a dielectric protective layer, a semi-conductor layer, a transparent electro-conductive layer, an anti-reflection layer, an optical interference layer, a hard coat layer, a subbing layer, and a barrier layer etc. are provided on a substrate, are used in a semi-conductor device or various kinds of devices for a displaying, recording or converting light to electricity.
These layers with high function are formed according to a dry coating method employing vacuum processing such as a spattering method, a vacuum depositing method or an ion plating method.
The vacuum processing requires a vacuum processing apparatus, resulting in high cost of the equipment. Further, the vacuum processing is difficult in continuous production, and low in a layer forming speed, resulting in disadvantage of lowering of productivity.
As a method for overcoming the disadvantage in that use of the vacuum processing apparatus results in lowering of productivity, an atmospheric plasma treatment process is proposed in Japanese Patent O.P.I. Publication No. 61-238961 in which generates a discharge plasma at atmospheric pressure to obtain a high processing effect by the discharge plasma. The atmospheric plasma treatment process can form a layer with a uniform composition, physical property or distribution on the surface of a substrate. Further, the atmospheric plasma treatment process can carry out the processing under at atmospheric pressure or approximately atmospheric pressure, and does not require a vacuum processing apparatus, it makes it possible to reduce the equipment cost, carry out continuous production, and increase a layer forming speed. A method is disclosed in Japanese Patent O.P.I. Publication Nos. 11-133205, 2000-185362, 11-61406, 2000-147209, and 2000-121804, which comprises subjecting a reactive gas to discharge treatment at atmospheric pressure or approximately atmospheric pressure, exciting the reactive gas to a plasma state and forming a layer on a substrate (hereinafter referred to also as an atmospheric pressure plasma method). The atmospheric pressure plasma method disclosed in these publications generates discharge plasma between two opposed electrodes by applying pulsed electric field with a frequency of from 0.5 to 100 kHz and with a strength of electric field of from 1 to 100 V/cm. Further, a method is disclosed in Japanese Patent O.P.I. Publication No. 6-330326 in which a metal alkoxide is added during atmospheric plasma discharge to form a metal oxide layer.
However, the metal alkoxide above, for example, an organic silicate compound, an organic titanium compound, an organic tin compound, an organic zinc compound, an organic indium compound, an organic aluminum compound, an organic copper compound, or an organic silver compound, is liquid under ordinary temperature whose vapor pressure is not so high. The alkoxide requires to be gasified by heating, mixed with inert gas such as argon or helium, and introduced to a discharge space between opposed electrodes. When the surface temperature of the electrode is lower than temperature of the mixed gas, the component such as the above metal oxide condenses on the electrode which causes the problems in that a mixed gas with a constant composition cannot be obtained, a uniform layer is difficult to obtain, and the condensed portions are reacted to form a solid, resulting in clogging of the gas path and contamination on the electrode surface.
The present inventors have succeeded to form a uniform layer with higher quality on a substrate rapidly by subjecting the substrate to plasma treatment applying a high frequency voltage exceeding 100 kHz at not less than 1 W/cm2. However, there occurs phenomenon in that continuous plasma discharge treatment employing such a high power shortens time when contamination begins to occur on the electrodes, and the contamination is more apparent, and further use of the electrodes with contamination deteriorates layer formation on the substrate, lowers quality of the formed layer, produces layer thickness variation, and lowers strength of the formed layer. Further, frequency of cleaning contamination increases, resulting in lowering productivity. When such phenomenon occurs during the manufacture, the manufacture is suspended to clean electrodes etc., conditioning and warm-up is carried out to restart the manufacture, which is time consuming and lowers production efficiency.
Heating the electrodes in order to prevent gas from condensing on the electrode is likely to induce non-uniform discharge due to dielectric breakage of the electrode which cannot form a uniform layer on the substrate.